1. Field of the Invention
The present invention relates to an image pick-up apparatus including thin film transistors (TFT's) and semiconductor conversion elements and a manufacturing method thereof, a radiation image pick-up apparatus, and a radiation image pick-up system.
2. Description of Related Art
Recently, the enlargement of the size of a TFT matrix panel, in which TFT's are formed on an insulating substrate, and the speeding-up of the drive speed of the panel have been rapidly promoted. Manufacturing methods of liquid crystal panels using thin film transistors (TFT's) are utilized as area sensors including semiconductor conversion elements for converting radiations such as X-rays to electric signals (for example, a radiation image pick-up apparatus). As such a semiconductor conversion element, for example, there is a conversion element in which a wavelength conversion layer (e.g., a phosphor layer) for performing a wavelength conversion from a radiation such as an X-ray to light such as visible light is arranged on the surface of the conversion element for performing the photoelectric conversion of the light. Another conversion element uses a semiconductor converting material for converting a radiation to an electric signal directly.
In a substrate arranging such semiconductor conversion elements and TFT's for reading out electric signals from the semiconductor conversion elements two-dimensionally thereon for reading the amount of irradiation of radiations, a radiation image pick-up apparatus having a high sensitivity can be provided by detecting a larger amount of a radiation or the light converted from the radiation which is irradiated to each pixel. For the sake of that, it is needed to arrange the conversion elements using the whole space effectively while keeping the performances of the TFT's.
Accordingly, a method of forming a TFT array before stacking conversion elements on the TFT array for improving the sensitivity thereof by preventing the loss of open area ratios of TFT's has been conventionally proposed. As an example, U.S. Pat. No. 5,498,880 discloses an arrangement of conversion elements above TFT's. A schematic sectional view of the prior art is shown in FIG. 20. FIG. 20 shows a configuration in which two pixels are laid side by side. One pixel is composed of a TFT 5 on the lower left side, a capacitor portion 6 on the lower right side, and a conversion element arranged thereon. The top surface of the TFT 5 is covered by an insulating layer 98 to remove unnecessary regions. By arranging the conversion element above the insulating layer, the prior art improves the open area ratio greatly.
However, the achievement of increasing the amount of signals, namely the reduction of the amount of noises, is needed together with the improvement of the open area ratio for improving the sensitivity. In other words, when noise components increase, an S/N ratio does not increase even if signal components are improved. The situation cannot be said that the actual sensitivity is improved.
FIG. 21 is a simplified equivalent circuit diagram showing the plane configuration of the example shown in the U.S. Pat. No. 5,498,880.
A charge capturing electrode 3n is not arranged on gate wiring 11 and signal wiring 13. Because the insulating film 98 is formed at the inside of the electrode 3n as shown in FIG. 20, it is known that the insulating film 98 is not formed on the gate wiring and the signal wiring.
When a capacitance applied to signal wiring and gate wiring becomes larger, the noises of an image to be taken in become larger in a radiation image pick-up apparatus. Accordingly, it becomes important to decrease the parasitic capacitance applied to both the wiring. In the example of the above-mentioned U.S. Pat. No. 5,498,880, the insulating layer 98 does not cover the gate wiring and the signal wiring, and consequently no measures for the parasitic capacitance of the signal wiring concerning noise components are considered. As a result, though the improvement of signal components owing to the improvement of the open area ratio can be recognized, noises are not considered, and consequently the sensitivity regarded as the S/N ratio is estimated to be insufficient.